Silicon is a promising high capacity anode material for lithium-ion cells but can suffer from poor cycle life and capacity fade (or loss of capacity upon each subsequent cycle) due to the high volumetric changes that can occur during lithium insertion/de-insertion.
Briefly, lithium-ion batteries are light weight, high energy, and long cycle life secondary (i.e., rechargeable) batteries. Lithium-ion batteries including non-aqueous electrolytes can be used as power sources for portable electronic devices such as notebook personal computers, mobile phones, digital cameras, camcorders and so on. These lithium-ion batteries are also being evaluated as power sources for hybrid electric vehicles (HEV) and plug-in HEV (PHEV).
Lithium-ion batteries are typically prepared from one or more lithium-ion cells containing electrochemically active materials. A cell generally includes a pair of electrodes (i.e., an anode and a cathode) and a separator that electrically separates the electrodes, but allows ions to pass through it. An electrolyte is dispersed within the cell to maintain charge balance during charging and discharging. The electrolyte can include a lithium salt (e.g., LiPF6) dissolved in one or more liquid solvents (such as aprotic organic solvents) or incorporated in one or more solid polymers (such as polyacrylonitrile). The anode of a lithium-ion cell can include an intercalation material. Examples of intercalation materials include carbonaceous materials, such as coke, mesocarbons (e.g., mesocarbon microbeads (MCMBs)), glassy carbons, amorphous carbon, and graphite. The cathode of a lithium-ion cell can include a lithium metal oxide, such as LiCoO2, LiNiO2, or LiMn2O4.
A lithium-ion cell typically is not charged in its initial condition. To deliver energy, such a cell is typically charged so lithium ions are released from the lithium-containing cathode, transferred to the anode, and intercalated at the anode. During discharge, a reverse process occurs to deliver an electrical current through an external load. Upon subsequent charge and discharge, the lithium ions are transported between the anode and cathode.